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Class _S^^M1 
Book. 1^4 



CfiPffilGHT DEPOSm 



The Preparation of Substances 
Important in Agriculture 



A Laboratory Manual of Synthetic 
Agricultural Chemistry 



THIRD EDITION 
BY 

CHARLES A. PETERS, Ph.Ei 

Professor of Inorganic and Soil Chemistry 

Department of General and Agricultural Chemistry 

Massachusetts Agricultural College 



NEW YORK 

JOHN WILEY & SONS, Inc. 

London: CHAPMAN & HALL, Limited 
1919 



^^1 



i 






COPTRIGHT, 1919, 
BY 

a A. PETERS 



v)A(\ ib \^\^ 



Stanbopc iprcss 

F. H.GILSON COMPANT 
BOSTON, U.S.A. 



'CI.A5 11329 



PREFACE 



It has been the aim in this manual to 
select substances of agricultural interest, 
adapt them to laboratory preparation, and 
explain their chemistry to the best of our 
present knowledge not overlooking their 
practical significance. 

The work was at first nothing more than 
laboratory directions, but the interest of the 
student gradually required the addition of 
explanatory matter to such a degree that 
the emphasis on an accompanying text has 
been greatly reduced. The method of pres- 
entation aims to put a few major points 
before the student and extend the work on 
such points over so long a time that the 
student will absorb it. The author feels 
that when a student, in his earlier years in 
college, works interestedly for a whole exer- 
cise around one thing he grasps something 
while if a dozen important points pass in 
review during the time he is left in a maze 
and gets little but technical benefit. While, 
however, the student is busy on the one 



iv Preface 

major piece of work other minor points may 
be gatherd around it and are readily ab- 
sorbd. 

In this collection of agricultural material 
it is interesting to note the points that are 
brot home to the student as the work 
develops Among these are oxidation, neu- 
tralization, distillation, crystallization, sat- 
uration, chemical calculations, metathesis, 
miass action, double salts, equilibrium and 
colloids. By making a process necessary 
to the production of material the student 
must grasp it or fail in the experiment. 
Take the seemingly simple matter of satura- 
tion. It is but the work of a minute to ex- 
plain what is meant by the process; the 
student will give an inteUigent expression of 
the phenomenon in a second minute ; how- 
ever, when in the laboratory he is making a 
preparation from two others, the success of 
which depends upon the preparation of two 
saturated solutions, then, and not until then, 
does the student understand saturation. 

Only about half of the students entering 
this college have had farm experience. It is 
difficult to interest a student in the prepara- 
tion of superphosphate or Bordeaux mixture 
unless he knows something of its use, hence 
the amount of space given in the notes to the 
p'-actical use of each substance. This does 



Preface v 

not lessen the value of the material for 
chemical instruction but rather enhances 
it. 

The work was designd for students in an 
agricultural college who have already had 
such a knowledge of chemistry as is acquired 
from a year's work in the high school. It is 
intended to be done in two or three hour 
laboratory periods, and furnishes sufficient 
material for one semester of such exercises. 
The arrangement of the work is such that a 
laboratory full of students can all be doing 
the same thing at the same time without 
extended waiting; procedures, such as crys- 
tallization and cooling, taking place in the 
interim between exercises. With us it is 
customary to score the preparation when 
completed, as one would butter or milk, 
allowing something for quahty and some- 
thing for quantity and to give credit for the 
exercise only upon completion of the prepara- 
tion. 

The author is endeted to Professor A. A. 
Blanchard of the Massachusetts Institute of 
Technology not only for the development of 
synthetic method of laboratory work for first 
year work in college, but also for the privilege 
to adapt three preparations from his book, 
Synthetic Inorganic Chemistry, for use in 
this manual. The three preparations are 



vi Preface 

Potassium Nitrate, Copper Sulfate and Lead 
Nitrate. 

The appreciation of the author is also 
exprest to Dr. H. S. Adams of New Bruns- 
wick, N. J., who was associated with this 
work in its early stages, and to Professor 
Ernest Anderson of this laboratory who has 
given this course for several years. Valuable 
suggestions have come from both these men. 

The first edition was printed privately in 
1914; the second was again mimeographed 
in 1916; the third is herewith offerd to those 
laboratories that have used the manual since 
1914 and to others that wish to experience 
the fascination of the synthetic method in 
agricultural chemistry. 

A few simplified spellings have been used. 

Amherst, Mass., 
August 1, 1918. 



CONTENTS 

Page 

Superphosphate 1 

SuL^TE OF Ammonia 13 

Potassium Nitrate 20 

Potash Salts 26 

Sulfate of Potash-Magnesia 26 

Sulfate of Potash (High Grade) 28 

Muriate of Potash 30 

Lead Nitrate 38 

Lead Arsenate 41 

Lime-Sulfur 50 

Copper Sulfate 69 

Paris Green 64 

Bordeaux Mixture 68 

Emulsions 78 



vii 



The Preparation of Substances 
Important in Agriculture 



SUPERPHOSPHATE 

Superphosphate is made from the natural 
rock phosphate, finely ground, and sulfiu"ic 
acid, the phosphate being acted upon as 
shown in equation (1) which follows: 

(1) CasPaOs + 2H2SO4 • aq = CaH4Po08 • H2O 
+ 2CaS04 • 2H2O. ^ai"^ 

Calcium sulfate (gypsum) dihydrogen 

phosphate 

Two-thirds of the calcium of the tricalcium 
phosphate are replaced by the hydrogen of the 
acid. Chamber sulfuric acid is used. It is 
necessary to calculate the actual amount of 
tricalcium phosphate in the material at hand, 
the amount of sulfuric acid to act on 200 
grams of this material and the amount of 
water that must be added to the sulfuric acii 
to make it of the proper strength. 

Calculations. — (a) Note the purity of 
the phosphate rock and calculate the number 
of grams (a) of the tricalcium phosphate in 
1 



2 Preparation of Substances 

200 grams of the material used. Record the 
amount. 

(6) From the equation given above cal- 
culate the number of grams (6) of H2SO4 
necessary to react with (a) grams of Ca3P208. 
Note the number. 

(c) Read the specific gravity of the 
chamber acid from the spindle floating in the 
acid on the side shelf Refer to the table of 
specific gravity and read off the weight of 
the H2SO4 in 1 cc. of the chamber acid. 
Calculate the number of cubic centimeters 
of chamber acid (c) necessary to contain 
the (h) grams of H2SO4. Record the 
volum. 

(d) The chamber acid is too strong to be 
used directly on the rock phosphate and must 
be diluted until it has the specific gravity 
1.53. Calculate the number of cubic centi- 
meters (d) of this acid necessary to contain 
(b) grams of sulfuric acid. This is the volum 
to which (c) cubic centimeters of chamber 
acid should be diluted before the rock phos- 
phate is added to it. Record the number. 

Tabulate the results of the four calcula- 
tions as indicated below and have them veri- 
fied by an instructor before proceding with 
the work. 



Superphosphate 3 

(a) Weight of Ca3P208 in 200 grams rock phos- 

phate, grams. 

(b) Weight of H2SO4 required for 200 grams rock 

phosphate, gram.s. 

(c) Volum of chamber acid required for 200 grams 

rock phosphate, cc. 

(d) Volum to which the (c) cc. of chamber acid must 

be diluted, cc. 

Procedure. — Measure out the volum (c) 
of chamber acid and pour it into (d-c) cubic 
centimeters of water in a porcelain dish. 
Weigh out 200 grams of the rock phosphate 
and stir it slowly into the acid. Let the 
mixture stay in the evaporating dish until 
the next exercise. The hydrofluoric acid 
fumes that arise are to be avoided. 

Notebook; Test for Soluble Phosphates. 
— Shake a little of the superphosphate with 
water, filter the solution, add to the filtrate a 
solution of ammonium inolybdate and warm 
the liquid gently in a test tube. If the yellow 
precipitate of ammonium phosphomolybdate 
does not form after a few seconds its ap- 
pearance may be hastend by adding a gram 
or two of solid ammonium nitrate. The 
addition of ammonium hydroxid followd 
by nitric acid will accomplish the same result 
including the heating; when this is done the 
solution must be left acidic with nitric acid. 

If some of the natural rock phosphate is 



4 Preparation of Substances 

treated similarly it will be seen that only an 
inappreciable amount of phosphate dissolvs 
in water. 

Test for Lime. — Dissolv some of the 
superphosphate in water and filter as before. 
To the clear filtrate add a solution of oxalic 
acid or ammonium oxalate. The white 
precipitate that forms is calcium oxalate 
which shows the presence of calcium com- 
pounds in solution. 

NOTES 
The Beaum6 hydrometer is an instrument 
for determining density that has wide indus- 
trial use. It is, however, unscientific as it has 

Sulfuric Acid. Specific Gravity op Aqueous Solu- 
tions 



Decrees BL 


Sp. gr. 


1 cc. contains grams 
H2SO4. 


50.0 


1.53 


0.957 


50.6 


1.54 


0.977 


51.2 


1.55 


0.996 


52.8 


1.56 


1.015 


52.4 


1.57 


1.035 


53.0 


1.58 


1.054 


53.6 


1.59 


1.075 


54.1 


1.60 


1.096 


54.7 


1.61 


1.118 


55.2 


1.62 


1.139 



two separate scales, one for liquids heavier 
than water and one for liquids lighter than 
water, the two having no relation. Further, 



Superphosphate 5 

neither scale bears any relation to true specific 
gravity. See Thorp, Inorganic Chemical 
Preparations, p. 32. 

The solubility of the natiu*al rock phosphate, 
or floats, in a short time under most soil 
conditions, is so sUght that it has become a 
common practise to '^dissolv" it, that is, 
to convert it into the water-soluble acid 
phosphate having only one-third of the ori- 
ginal amount of calciimi. Under ordinary 
business conditions one-half of all the sul- 
furic acid made in this country is used in this 
process. 

Tricalcium phosphate, whether as rock 
phosphate, bones or the mineral apatite, is 
always associated with fluorin and generally 
chlorin. In addition rock phosphate is gen- 
erally associated with calcium and magnesium 
carbonates and sometimes iron and alumi- 
num phosphates so that the reactions which 
take place with the sulfuric acid are more 
complicated than that given at the beginning 
of this exercise. The following are the more 
important : 

(2) 2Ca3P208 . Ca2FP04 -f 7H2SO4 • aq = 

3CaH4P208 • H2O + 7CaS04 • 2H2O 
+ 2HF. 

(3) CaCOs + H2SO4 . aq = CaS04 • 2H2O 

+ CO2. 

(4) 2AIPO4 -h 3H2SO .aq = 2H3PO. -i- 

2A1(S04)3 • I8H2O. 



6 Preparation of Substances 

The fertiUzer manufacturer must determin 
the exact amount of sulfiu-ic acid to be used 
for each substance present in the ground rock. 
The student is not askt to do this. How- 
ever, to insure the presence of sufficient acid 
to combine with all these substances, the 
calcium phosphate content of the floats as 
given to the student is increased 5 to 10 per 
cent. 

The strength of sulfuric acid used will vary- 
according to the source and composition of 
the natural rock. If large amounts of cal- 
cium compounds other than phosphate are 
present a more dilute acid is used so that 
there will be water enuf to hydrate the 
land plaster (calcium sulfate) formd in the 
reaction. 

The calcium fluorid present reacts with 
the sulfuric acid producing the disagreeable 
poisonous hydrofluoric acid gas. Avoid 
breathing the fumes from the mixture. 

Notice that after standing the mass crum- 
bles easily in the hand. After storing several 
weeks, during which time the action of the 
sulfuric acid continues until the insoluble 
phosphates are reduced to a fraction of one 
per cent, the material is ground, if necessary, 
and put on the market or used as a ''base," 
i.e., one of the substances from which fer- 
tilizers are made. 



Superphosphate 7 

There being several calcium compounds in 
the rock phosphate which all appear finally 
as hydrated calcium sulfate (gypsum) it is 
not strange that the resulting superphos- 
phate is composed of 60-70 per cent of 
gypsum. From this it is easy to see why 
superphosphate contains only 14 to 16 per 
cent of phosphoric acid (P2O5). 

The deposits of rock phosphate at present 
being extensivly workt are found in South 
Carolina, Florida and Tennessee. The larg- 
est and most newly discoverd deposits are 
in Idaho, Utah and Wyoming. 

A good grade of ground rock carries 65 per 
cent of tricalcium phosphate and the material 
not infrequently runs over 80 per cent. In- 
ferior rock containing a few per cent of 
phosphoric acid and mixt with carbonate 
of lime is abundant, but it is not economical 
to ship this any great distance or treat it 
with sulfuric acid. 

The use of " raw rock '' vs. ''dissolvd rock " 
is a much discust question in agriculture. 
Thru the East, on Hght soils and for intensiv 
cultivation, the dissolvd rock is used ex- 
clusivly; for some of the heavy soils of the 
West raw rock is recommended in connection 
with decaying organic matter. According to 
Professor Hopkins of Illinois the raw rock in 
a heavy soil is converted to dissolvd rock 



8 Preparation of Substances 

by acid in the soil, the steps in the process 
being first, the production of ammonium 
carbonate, (NH4)2C03, from the amino 
groups, — NH2, in the plant; second, the 
oxidation of ammonia to nitrous acid by 
bacteria; third, the conversion of the raw- 
rock to dissolvd rock by the action of the 
nitrous acid which may be represented by 
the equation, 

Ca3P208 + 4HNO2 + H2O = CaH4P208 • H2O 

+ 2Ca(N02)2; 

and fourth, the oxidation of the calcium 
nitrite, Ca(N02)2, to calcium nitrate, 
Ca(N03)2, by the action of bacteria. Both 
the acid phosphate and the calcium nitrate 
resulting from the action are available to the 
plants for food. Naturally the plants richest 
in amino groups, such as clovers and alfalfa, 
are most desirable to plow under with the 
raw rock. This action of the dissolving of 
raw rock by acid in the soil has been demon- 
strated by Professor Hopkins in the labora- 
tory, but others deny that it actually takes 
place in the soil. 

As a general conclusion it may be said 
that all the phosphorus of acid phosphate 
is immediately available to plants while only 
a small amount of the phosphorus in the 
raw rock is available during one growing 



Superphosphate 9 

season; however, the phosphorus in raw rock 
continues to become available, year by year, 
until the total amount is drawn upon. For 
cultural purposes the important question is 
whether or not there is sufficient phosphorus 
available in one season for the crop in ques- 
tion; this, of course, depends upon many 
factors which cannot be gone into here. 

Analysis of Rock Phosphate. — An analy- 
sis of Tennessee rock phosphate taken from 
the American Fertilizer Handbook for 1908 
is here given: 

Per cent 

Moisture (loss on drjdng) 0.87 

Combined water and organic "matter 

(loss on ignition) 1 . 53 

Sand and insoluble matter 2.76 

Ferric oxid, Fe203 2.40 

Alumina, AI2O3 1 . 99 

Lime, CaO 49.07 

Magnesia, MgO 0. 24 

Carbon dioxid, CO2 1.08 

Fluorin, F 2.98 

Sulfur trioxid, SO3 1.03 

Phosphoric acid, P2O5 35.62 

99.57 

When these figures are put together in an 
attempt to show the substances that existed 
in the original rock the data shown under 
colum (a) is obtaind. The composition of 
another sample of rock phosphate is shown 



10 



Preparation of Substances 



in colum (6). It is noticeable that many 
of the constituents vary widely in quantity. 





(a) 


ib) 


Moisture and organic matter 

Phosphate of lime, Ca3P203 

Phosphates of iron and aluminium 
FeP04, AIPO4 


Per cent 

2.30 

77.76 

4^43 
0.50 
6.11 
0.77 

1.88 

1.99 

2.76 

98.60 


Per cent 

1.00 
55.00 

6.50 


Carbonate of lime, CaCOa 

Carbonate of magnesia, MgCOs . . . 
Fluorid of lime, CaF2 


3.50 
0.75 
2.25 


Iron pyrites, FeS2. . 




Iron oxid, Fe203. . . 




Alumina, AI2O 




Sand and silicious matter 


28.00 
100.00 



The natural sources of phosphorus are 
the mineral apatite, or phosphorite, which is 
an ingredient of nearly all soils. It has the 
same formula as the raw rock phosphate but 
is entirely different in appearance. Immense 
deposits of this mineral are localized in 
Quebec and Ontario, Canada. 



QUESTIONS 
(To be answerd in the notebook.) 

1. What is the per cent of P2O5 in calcium dihy- 
drogen phosphate? 

2. Supposing equation (2) to represent all that 
happens when sulfuric acid acts upon rock phosphate, 
calculate the per cent of hydrated acid phosphate and 
the per cent of hydrated calcium sulfate in the 
mixture. 



Superphosphate 11 

3. Again supposing equation (2) to represent what 
happens when superphosphate is made, what is the 
highest per cent of P2OS it is possible to have in super- 
phosphates? 

4. What per cent of P2O5 is present in ordinary 
superphosphate? Name the substance represented by 
the symbol P2O5. 

5. What per cent of tricalcium phosphate is found 
in natural phosphates? 

6. Which would use the more sulfuric acid, a raw 
rock carrying 60 per cent tricalcium phosphate and 
5 per cent calcium carbonate or a rock carrying 55 per 
cent tricalcium phosphate and 10 per cent calcium 
carbonate? 

7. What gases escape during the action of the sul- 
furic acid on the rock phosphate? Which is poison- 
ous? 

8. What compounds are found in the raw rock? 
In the dissolvd rock? The student cannot give, for 
example, calcium oxide, CaO, or phosphorus pentoxid, 
P2O5, as compounds present in either the raw or dis- 
solvd rock altho such compounds are well known and 
moreover are represented in the table of analysis. In 
the raw and dissolvd rocks the lime and the phosphoric 
acid are in combination and the student should give, 
as well as he can, the actual lime and phosphorus com- 
pounds that are present. 

9. How could phosphoric acid be made by a process 
similar to that for making superphosphate? 

10. How could the acid phosphate be made into a 
neutral salt? How would the solubility change? 

11. Write a symbol for another acid calcium phos- 
phate; name the compound. 

12. How is the test made for soluble phosphate? 

13. Describe the test for lime. 



12 Preparation of Substances 

14. How many grams of actual sulfuric acid in a 
liter of dilute acid of a density of 51.5 Be.? 

15. Where are the phosphate deposits in this 
country? 

16. Where should a plant for making superphosphate 
be located? Near the phosphate mines or near the 
farmer? Give reasons for the answer. 

17. What is meant by the terms, " raw rock," " dis- 
solvd rock " ? 

18. Where is the use of dissolvd rock recommended? 

19. Is calcium sulfate soluble in water? (See text 
under calcium compounds.) 

20. Write symbols for limestone; slaked lime; quick- 
lime. 



SULFATE OF AMMONIA 

Sulfate of ammonia is made by distilling 
the ammonia from the gas liquor into sulfuric 
acid. The first problem is to find out, ap- 
proximately, how much gas liquor should be 
used to neutralize a convenient amount, say 
15 cc, of chamber sulfuric acid. 

Calculations. — Read the specific gravity 
spindle floating in the sulfuric acid and cal- 
culate, from the table on page 4, the amount 
of actual sulfuric acid in the 15 cc. to be used. 
From the equation, 

2NH3 + H2SO4 = (NH4)2S04, 

find out how many grams of ammonia are 
necessary to unite with this amount of acid. 

Ascertain the strength of the gas liquor 
and compute the volum necessary to con- 
tain the desired amount of ammonia. 

For example: If 30 grams of ammonia 
(NH3) are desired and the gas liquor is 8 per 

cent ammonia, there will be -— — = 125 grams 

(J. 08 

required. The density of gas liquor being 

nearly the same as water, 125 cc. in place 

of 125 grams may be considerd the correct 

amount. 

13 



14 Preparation of Substances 

Enter the results as given below and have 
them verified by an instructor. 

Amount of actual acid in 15 cc. of chamber acid, . .grams. 

Amount of ammonia equivalent to the acid, grams. 

Volum of gas liquor to contain the ammonia, cc. 

Procedure — Arrange a distilling appa- 
ratus consisting of a flask of a capacity of 
from 500 to 1000 cc. carrying a two-hole rub- 
ber stopper. Thru one hole put a thistle 
tube reaching to within 1 cm. of the bottom 
of the flask, thru the other hole insert a 
bent tube carrying a one-hole stopper fitted 
to a condenser. Put 15 cc. of chamber sul- 
furic acid into a 250-cc. gas bottle and adjust 
to the delivery tube of the condenser so that 
the bottle rests on the desk and the delivery 
tube dips under the acid. Draw from 10 
to 50 cc. more than the calculated amount 
of gas liquor, — the amount depending 
on its strength, — pour it thru the thistle 
tube into the flask and begin heating. As 
soon as the distillation is well under way, 
look for the deposit of ammonium carbonate 
in the condenser. If any appears — as it 
always does — it will be necessary to break 
up this compound in the flask by adding lime. 
To do this make a paste of 10 to 15 grams of 
lime and 50 to 75 cc. of water and pour 
the mixture, which is milk of lime, thru a 



Sulfate of Ammonia 15 

piece of cheese cloth placed over the thistle 
tube. The reaction results in the precipi- 
tation of calcium carbonate in the flask, 

Ca02H2 + (NH4)2C03 = CaCOs + 2NH3 
+ 2H2O, 

and the liberation of ammonia which vola- 
tilizes faster than the ammonium carbonate. 

When the sulfuric acid is entirely neutra- 
lized, as is shown by the action of litmus 
paper or a decided change in the appearance 
of the distillate, disconnect the apparatus. 
Filter the solution of ammonium sulfate in 
the gas bottle if tarry matter has collected in 
it, first making sure that all the ammonium 
sulfate is in solution, and evaporate the clear 
filtrate in a porcelain dish to the point of 
crysta'lization. 

Cool the mixture, bring the mass of crystals 
on a paper filter and allow them to drain and 
further dry by pressing between filter papers. 
Weigh the crystals and enter the amount in 
the notebook. 

To become familiar with the properties of 
the salt, heat a little in a dry test tube and 
hold a piece of moistend red litmus in the 
mouth of the tube. Ammonium sulfate 
melts at 140°; at 280° it decomposes, losing 
ammonia and leaving behind ammonium 
acid sulfate. 



16 Preparation of Substances 



NOTES 

The time of the student is such an impor- 
tant factor that considerable more than the 
required amount of ammonia is recommended 
for use. This obviates waiting for all the 
ammonia to be driven off and also saves 
evaporation of the increased amount of water 
which would distil over. Of course a waste 
of ammonia results. Industrially such a 
waste of ammonia would not be allowd. 

If the evaporation procedes beyond a cer- 
tain point the mass upon cooling will be solid 
salt. In this case filtering and drying are 
unnecessary. The danger in using this 
quicker method of drying lies in the fact that 
the solution of ammonium sulfate in water 
upon being heated to dryness passes over into 
a clear molten anhydrous mass so quickly that 
the change may not be noticed. Heating this 
molten anhydrous mass results in the decom- 
position of the salt as explaind in a previous 
paragraf. 

In the manufacture of coal gas, by heating 
soft coal much of the nitrogen present is 
combined with hydrogen forming ammonia. 
Some of the oxygen that enters the retorts as 
they are charged combines with the carbon 
forming carbon dioxid. This weak acid, 
carbonic acid, unites with the weak base 



Sulfate of Ammonia 17 

ammonia and forms the volatil salt, am- 
monium carbonate. Part of the process of 
purification of coal gas consists in washing 
out the ammonia and ammonium carbonate 
in water. This wash is known as dilute gas 
liquor (2f oz. of ammonia to the gallon) 
and may be concentrated by distillation. 
Such a concentrated product contains the 
equivalent of about 18 oz. of ammonia 
(NH3) per gallon of liquid. 

The United States normally produces 
about 300,000 tons of sulfate of ammonia 
annually. Since the war the production has 
doubled and is constantly increasing. It is a 
plant food furnishing both nitrogen and sulfur; 
excessive use as a fertihzer, however, may 
deplete the soil of its calcium. 

The milk of lime which decomposes the 
ammonium carbonate must be straind or 
the lumps will clog the thistle tube. In 
place of the procedure described the mixture 
may be allowd to settle four or five seconds 
after stirring and the upper portion pourd 
thru the thistle tube leaving the lumps be- 
hind on the bottom of the container. 

Should the process of distillation be inter- 
rupted before the sulfuric acid is neutral- 
ized the product will be a mixture of the 
neutral and acid ammonium sulfates. 

Sometimes the tarry materials exist in the 



18 Preparation of Substances 

neutralized solution in colloidal condition 
and are not flocculated imtil the ammonium 
sulfate solution has become more concen- 
trated. Should flocculation occur during the 
course of evaporation the tarry substance 
then may be filterd out. It is this material 
left in the preparation which gives the pecu- 
liar brownish color to commercial sulfate of 
ammonia. 

The point of crystallization is determind 
by blowing across the surface of the hot 
liquid. When a scum appears at once the 
evaporation by flame may cease. 

QUESTIONS 
(To be answerd in the notebook.) 

1. How many grains of ammonia in 2 kilos of a solu- 
tion containing 28.33%? 

2. How much ammonia in 250 cc. of a solution of a 
sp. gr. of 0.970 containing 7.31% of NH3? 

3. How many tons of ammonium sulfate could be 
made from a tank car of concentrated ammonia con- 
taining 5000 gallons of 14% NH3? The weight of a 
gallon may be taken as 8 pounds. What is this worth 
at $60.00 per ton? 

4. What is the per cent of ammonia in ammonium 
suKate? 

5. Write the reactions, giving] the names, showing 
how two different salts may be made by puttuig to- 
gether ammonimn hydroxid and sulfuric acid. 

6. What other substances in addition to ammonia 
are produced by distilling soft coal? 



Sulfate of Ammonia 19 

7. What is the use of the lime in the distillation of 
gas liquor? 

8. Explain the presence of annnonium carbonate in 
gas liquor. 

9. Why is commercial sulfate of ammonia brown? 
10. Why does a brown substance sometimes settle 

out during the concentration of the ammonium sul- 
fate solution? 



POTASSIUM NITRATE 

Potassium nitrate is made by metathesis of 
potassium chlorid and sodium nitrate, taking 
advantage of the different solubiUties of the 
four possible salts in hot and cold water. 

Procedure. — Heat 200 cc. of water in a 
porcelain dish and when hot add 100 grams 
of sodium nitrate and 90 grams of muriate 
of potash. Evaporate until the volum is 
reduced to about 100 cc, and filter off the 
sodium chlorid, sand and dirt thru a 
carefully prepared Witt filter. Throw away 
the residue on the filter, and cool the fil- 
trate until the crystals of potassium nitrate 
appear in quantity. 

Some care is required to judge when the solution is 
boild down to one-haK its original volum. If it is 
filterd too soon, in which case few or no potassium 
nitrate crystals separate out of the filtrate on cooling, 
the filtrate should be evaporated further and again 
filterd to remove the sodium chlorid which will sepa- 
rate as solution boils away. If the mixture boils too 
long before filtering the crystalhzation of the potas- 
sium nitrate will take place in the funnel stem and 
clog the filter. In such a case the whole mass should be 
put back in the dish with about 50 cc. more of water 
and reheated. It sometimes aids the filtering to warm 
20 



Potassium Nitrate 21 

the funnel just previous to using. This can be done 
by pouring a test tube of hot water thru the funnel. 
Empty out the water. 

Filter off the crystals of potassium nitrate 
when the solution is cold; set the crystals 
aside. Evaporate the filtrate again until 
reduced about one-half its volum, or until 
crystals of sodium chlorid appear in quan- 
tity, filter thru the Witt plate, rejecting 
the sodium chlorid on the filter and cool the 
filtrate to the lowest point possible to crystal- 
lize the potassium nitrate. Filter off this 
crop of potassium nitrate, and put with 
the quantity previously obtaind. As both 
crops of crystals came from a solution 
saturated with sodium chlorid as well as 
potassium nitrate and as sodium chlorid is 
slightly less soluble (4 grams per 100 cc.) in 
cold water than hot some sodium chlorid 
crystals will have formd on the nitrate. To 
get rid of these, dissolv the nitrate in hot 
water, using about 50 cc. or less for every 
100 grams of crystals, and cool in cold water 
as was done before. Filter. The mother 
liquor should contain all the sodium chlorid 
and if the mother liquor adhering to the 
crystals on the filter can be replaced by water 
before they dry out the product will be free 
from chlorid. Wash the crystals with cold 
water, a drop at a time, until a few of the 



22 Preparation of Substances 

crystals in water in a test tube give no test 
for chlorin ions when a soluble silver salt is 
added. 

The microscope can be used to advantage here. 
If square right angle blocks (sodium chlorid) are 
formd adhering to the long nitrate bars the crystals 
will have to be redissolvd. If no blocks of sodium 
chlorid are seen it may be taken for granted that 
purification may be brot about by continued, drop by 
drop, washing with cold water. The crystals when 
pure may be dried by pressing between filter paper or 
by allowing to stand over one exercise. 

NOTES 

The Witt filter consists of a perforated 
porcelain disk in a funnel fitted into a 
heavy glass suction flask, having connection 
with an aspirator. It is a convenient 
and rapid means of filtering when prop- 
erly used. The student should be supplied 
with paper filters of a diameter about one 
centimeter greater than that of the porcelain 
plate. Should the plates become chipt they 
can still be used if a small piece of filter 
paper is torn off and laid over the damaged 
place. Unless the chipt place is so closed 
pressure will make a hole in the filter paper 
allowing the precipitate to pass thru into the 
filtrate. 

The flask should be supplied with rubber 
tubing of ordinary thickness, not pressure 



Potassium Nitrate 23 

tubing, and a pinchcock to help regulate the 
pressure. The proper use consists in ar- 
ranging the apparatus, starting the pump, 
emptying the mixture on the filter, closing 
the rubber tube with the pinchcock and 
then shutting off the water. As the vacuum 
in the flask is relieved it can be increased by 
starting the pump and momentarily opening 
the pinchcock. Too much use of the pump 
is to be avoided. 

It is only in exceptional cases where potas- 
sium nitrate is of agricultural importance. 
True, it contains both potash and nitrogen in 
one compound and therefore in concentrated 
form, but these substances are as well sup- 
plied in agriculture by the sodium nitrate and 
the potassium chlorid separately. In isolated 
localities where the freight rate is exception- 
ally high it is possible that the cost of manu- 
facture of potassium nitrate would be less 
than the freight on the sodium chlorid elimi- 
nated in the process. In such a locaUty it 
might be desirable to use potassium nitrate 
for fertilizer. 

The classic use of potassium nitrate is for 
black powder. Sodium nitrate being hygro- 
scopic does not make a powder suitable for 
use in fire arms; however a coarse blasting 
powder is made from it, the large grains 
being glazed to keep out moistm-e. 



24 Preparation of Substances 

When the two salts are dissolve! in water 
all four ions, K+, Na+, CI", NOs", exist as 
well as all possible combinations of these. 
As water evaporates the least soluble com- 
bination of ions, sodium chlorid, will come out 
of solution tirst, so that the reaction procedes 
by metathesis, 

KCl + NaNOa = KNO3 + NaCl. 

It is to be noted in this reaction that as the 
Na and CI ions form the least soluble sub- 
stance so do the two ions remaining after 
these unite, K+ and NO3-, form the most 
soluble combination. Either circumstance 
would be sufficient to determin the direc- 
tion of the reaction. 

The change in solubility of the potassium 
nitrate in hot and cold solution is very great. 
When hot potassium nitrate is many times 
more soluble than sodium chlorid; at 33°, 
their molar solubilities are equal and below 
that temperature potassium nitrate is less 
soluble, being about one-half that of sodium 
chlorid at 10°. 

A graphic representation of the solubilities 
of these salts will be of aid to the student. 
Such figures are found in the following texts : 
Kahlenberg, p. 435; Alexander Smith, p. 131; 
Blanchard, Synthetic Inorganic Chemistry, 
p. 26. 



Potassium Nitrate 25 

QUESTIONS 
(To be answerd in the notebook.) 

1. How many grams of potassium chlorid are 
required to unite with 100 grams of sodium nitrate? 
Keep one decimal pkce in the figure. 

2. Of what use is potassium nitrate? 

3. Write the symbols of the four salts that exist 
in sohition at the beginning of this experiment. Write 
symbols for the ions. 

4. What is the solubility of potassium nitrate at 
100°? of sodium chlorid? 

5. What is the solubilitj^ of these two salts at room 
temperature or the temperature of hydrant water? 
State the exact temperature selected. 

6. Describe a test for chlorid ions. 

7. Describe the crystals of potassium nitrate; of 
sodium chlorid. 

8. When might it be desirable to use potassium 
nitrate as a fertilizer? 

9. Where is sodium nitrate found? What is its 
common name? Why is it not used for making gun 
powder? 

10. If one kilo of a solution of salt saturated at 100"* 
is coold to 10° how many grams of salt will separate 
out? Consult the rrafs in one of the references given 
in the last paragraf before the question. 



POTASH SALTS 

PART I 
SULFATE OF POTASH-MAGNESIA 

The sulfate of potash-magnesia is made 
according to the equation, 

3KC1 + 2MgS04 • H2O + IIH2O = K2SO4 . 
MgS04 . 6H2O + KCl . MgCl2 . 6H2O, 

by mixing saturated brines of potassium 
chlorid and magnesium sulfate. 

Procedure. — Weigh out 60 grams of 
muriate of potash and add it, as fast as it will 
dissolv, to about 100 cc. of boiling water. 
Making sure that all the salt is in solution 
filter the mixture while hot through a Witt 
plate to separate the iron oxid, dirt and sand. 
Put the filtrate in a beaker, keep the liquid 
at boiling temperature, and concentrate the 
brine until crystals of potassium chlorid begin 
to appear on the surface, showing that the 
solution is saturated at that temperature. 

While the foregoing is in operation weigh 
out 100 grams of kieserit and dissolv it in 
about 75 cc. of boiling water, adding the 
salt slowly. In case it does not all go into 
solution, indicated by a residue of salt on the 

26 



Sulfate of Potash- Magnesia 27 

bottom of the beaker and a scum on the 
surface of the Hquid, add 10 or 20 cc. more 
of water and heat, repeating the addition of 
small amounts of water and heating, if 
necessary, until the magnesium sulfate is 
all dissolvd. Filter, using the Witt plate, 
and concentrate the clear filtrate until the 
liquid is saturated as indicated by the for- 
mation of a scum on the surface. Mix 
the two hot saturated salt solutions and set 
the mixture aside for at least twelve hours. 
Both the solutions must be saturated upon 
mixing or the experiment will be a failure. 
The crystals that begin to form upon put- 
ting the solutions together and which further 
separate on cooling are the double sulfates of 
potassium and magnesium, K2SO4 • MgS04* 
6H2O, sometimes cald the sulfate of potash- 
magnesia. 

After the mixture has stood, filter off the 
crystals, drain them well on a Witt plate, 
transfer them to a paper and weigh. Save 
the filtrate which contains a solution of arti- 
ficial carnallit. 

The crystals of double sulfate may be dried 
in a few hours by spreading on paper when 
the exact weight may be obtaind or the 
approximate weight may be had at once, 
assuming that 5 to 6 per cent of the weight is 
water adhering to the crystals. 



PART II 
SULFATE OF POTASH, fflGH-GRADE 

It is customary to make sulfate of potash 
from the double salt by adding sufficient 
potassium chlorid to carry on the following 
reaction: 

3KC1 + K2SO4 . MgS04 . 6H2O = 2K2SO4 + 
KCl . MgCl2 • 6H2O. 

Procedure. — Calculate the amount of 
potassium chlorid necessary to react with 
the amount of double salt at hand, and weigh 
out enuf muriate of potash to furnish this 
amount of actual salt, allowing for impurity. 
Heat the necessary amount of water to boil- 
ing, dissolv the salt, filter off the dirt on a Witt 
plate, and heat the filtrate until it is satu- 
rated all as previously described mider sul- 
fate of potash-magnesia. 

Add the sulfate of potash-magnesia to 
boiling water, using 100 cc. for every 80 grams 
of salt, and put this mixture with the hot 
saturated solution of the chlorid. Potas- 
sium sulfate begins to separate at once and 
continues to come out on cooling. After 
standing 24 hours the salt may be filterd off 

28 



Sulfate of Potash, High-Grade 29 

and dried in the air. Record the weight of 
dried salt. 

The filtrate, which should be saved, also 
contains the double chlorids of potassium and 
magnesium (carnallit) similar to that obtaind 
under Part I. 



PART III 
MURIATE OF POTASH 

Procedure. — Put the two filtrates contain- 
ing the artificial carnalht brine together and 
evaporate the water until the hollow octahe- 
dral crystals of potassium chlorid appear in 
abundance. The decomposition of the car- 
nallit yields some potassium chlorid which 
crystalUzes out first; this is rapidly followd 
by the clear dense crystals of the carnallit 
itself. The latter may compose the major 
portion of the precipitate. If too much or 
nearly all the water is evaporated off mag- 
nesium chlorid will separate out making the 
product dehquescent. The crystals may be 
separated from the magnesium chlorid brine 
by the use of the Witt plate. The filtrate 
containing the solution of magnesium chlorid 
may be thrown away. 

The two salts, sulfate of potash and muri- 
ate of potash, dried and weighd, are handed 
in separately. 

NOTES 

The amount of water used to dissolv 
the salts may be quite a little more than 
would be calculated from the solubility 

30 



Muriate of Potash 31 

tables. There are several reasons for this. 
First, there are impurities present which if 
they contain an ion in common with the 
principal salt may necessitate the use of more 
water. To illustrate this suppose there are 
10 grams of sodium chlorid in every 50 grams 
of the crude potassium chlorid (a chlorid ion 
in common), then it is necessary to furnish 
water for the sodium chlorid as well as for 
the potassium chlorid; while if 10 grams of 
calcium nitrate were present (no common ion : 
K+, Ca+, NOs", C1-) this substance would 
dissolv in the solution already saturated with 
potassium chlorid. Second, sufficient water 
should be present so that the solutions may 
be filterd before they approach saturation; 
otherwise the crystallization that results on 
cooHng clogs the filter and causes delay. 

In filtering all such mixtures which con- 
tain fine sediment, first allow them to settle 
and bring the solid matter onto the filter 
only at the end of the operation after the 
clear liquid has past thru the filter. 

Kieserit, the magnesium sulfate with one 
molecule of water, is the salt that has sepa- 
rated out in the German deposits. Ordinarily 
from water the heptahydrate, MgS04 • 7H2O, 
separates out. Epsom salts, the hepta- 
hydrate, are made from kieserit by dissolving 
kieserit and allowing the salt to crystallize. 



32 Preparation of Substances 

In all this work it is the object to precipi- 
tate a salt by mixing two hot saturated solu- 
tions. The appearance of crystals or a scum 
(film of fine crystals) on the surface may be 
taken as an indication of saturation. Mixing 
solutions which are not saturated may result 
in large loss of the desired substance. Often 
the addition or withdrawal of one cubic 
centimeter of water is all that is necessary 
to produce the condition sought. 

In dissolving the double sulfate in water the 
salt may not appear to dissolv completely. 
This is immaterial as the residue is potassium 
sulfate, the same as the desired product. It 
is possible to crystallize out potassium sul- 
fate by evaporating the solution of potash- 
magnesia sulfate. 

Muriate of potash is sold in three grades 
containing 80, 95 and 98 per cent, respec- 
tively. The material containing 80 per cent 
potassium chlorid is the grade mostly used 
for fertilizers. This is produced industrially 
by treating the raw salts as they are mined 
with a hot saturated solution of magnesium 
chlorid such as is thrown away at the end 
of this experiment. The resulting hot solu- 
tion is coold in cement tanks and the crude 
muriate of potash separates out. The crys- 
tals are centrifuged and further dried over a 
fire in sloping pans about 10 X 60 feet in 



Muriate of Potash 33 

size. Bromin is obtaind from the magne- 
sium bromid in the spent magnesium chlorid 
brine. 

In former years one of the salts mined 
extensively in Germany was carnallit in a high 
degree of purity. Such deposits are no longer 
available, and in its place the carnallit brine 
appears from which the high grade, 96 to 98 
per cent, muriate of potash is made by con- 
centration and crystallization. 

The American sources of potash which 
have been investigated since 1908 and devel- 
oped since the war are the giant kelps of the 
Pacific coast, the nativ potash-bearing rocks, 
the products of blast furnaces and cement 
kilns and the salts of inland lakes. A brief 
discussion of each source is given. 

The kelps exert a selective action on the 
salts in the sea and take up relatively more 
potassium chlorid than other compounds. 
When the kelp is dried and incinerated the 
ash contains 15 to 50 per cent muriate of 
potash. The cost of production is so high, 
however, that the procedure is not economi- 
cal. On the other hand an ingenious fer- 
mentation process has been devised, pro- 
ducing acetone and esters as the principal 
products and potash as a by-product. This 
is in successful operation on the Pacific coast. 

The amount of potash in such minerals as 



34 Preparation of i:substances 

feldspar is unlimited, but here again the 
cost of production is so great that little 
potash is, as yet, produced from this source. 
Another mineral containing large quantities 
of potash is found in Utah and called alunite. 
This substance contains silicates and sul- 
fates of potassium and aluminium which on 
heating furnish water soluble sulfate of pot- 
ash. Six hundred tons a month of potas- 
sium sulfate were being produced in 1918 
from this source. 

Potash is being produced in this country, 
England and France from the blast furnaces 
of the steel industry. The limestone, iron ore, 
and coke used in the smelting may each con- 
tain some potash; if so during the heating 
some of this is volatilized. Special devices, 
electrical precipitators, take the potash-bear- 
ing dust out of the gases as they pass from the 
furnaces. Potassium chlorid is the substance 
obtaind. As there is generally insufficient 
chlorin to combine with the potassium the 
amount of substance volatilized is limited by 
the chlorin available. The addition of com- 
mon salt, sodium chlorid, to the furnace 
charge consequently increases the amount 
of potash recoverd. It is said that there is 
sufficient potash available from this source to 
furnish the entire needs of this country. 

The cement kilns also volatilize potassium 



Muriate of Potash 35 

chlorid from potash compounds present in 
the hmestone and sihcates used in their 
manufacture. The material is very fine and 
would be lost as " smoke " if the particles 
were not charged with electricity and then 
caused to deposit on strong electrically 
charged plates in the Cottrell process of 
electrical precipitation. 

Searles Lake in the California desert con- 
tains over 12 square miles of a crystal de- 
posit 70 feet thick. These crystals are 
surrounded by a saturated brine carrying 
about 5 per cent of potassium chlorid. The 
brine contains two bases, sodium and potas- 
sium; and four acids, chlorides, sulfates, 
borates and carbonates. Potassium chlorid 
and borax are the products of this industry. 
It is calculated that there are 30 miUion 
tons of potash in this region which in itself 
is sufficient to supply the needs of America 
for 25 or more years. 

The work outlined in this exercise deals 
with double salts occasiond by the presence 
of magnesium when the magnesium is absent, 
as in most of the American deposits, the 
process of crystalhzation is much simphfied. 

The size of the crystal generally varies 
with the rapidity with which it forms. If 
the salt forms quickly, the crystals are small; 
if more slowly, the crystals are larger. 



36 Preparation of Substances 

' Each of the crystals has its definit shape which is 
easily seen under the microscope. Reference is given 
to various figures of crystals in Watt's Dictionary of 
Chemistry, Vol. II, pages 148 ff. 

The hydrated double sulfate of potassium and mag- 
nesimn is inclined to form coarse monoclinic prisms 
which loik hke half cubes or diamonds which have 
been prest so that the upper faces are not directly over 
the lower ones. Compare Figs. 285 and 287. 

Potassium chlorid, hke sodium chlorid, appears in 
cubes or colums, or commonly as a four-sided funnel 
or hollow pyramid. 

Potassium sulfate may be in small hexagonal prisms 
(really rhombic) or in longer prisms with a bluntly 
tapering end. Vid. Figs. 272 and 297. Sunilar figures 
are shown in Gmehn-Kraut, Vol. 2i, p. 49. 

Magnesium sulfate is inclined to grow in long 
needles (rhombic) with faces on the very abrupt end. 
Vid. Fig. 281. 

Magnesium chlorid, MgCl2 • 6H2O, forms mono- 
chnic prisms much like the double sulfate of potash- 
magnesia. Vid. Figs. 285 and 287. 

QUESTIONS 
(To be answerd in notebook.)] 

1. Calculate the per cent of potash, K2O, in the 
sulfate of potash-magnesia; in potassium sulfate; in 
potassium chlorid. Express results as follows: 

K.0 94.3 ^ ^^^^^^^ 



K2SO4 174.4 

2. Tell when a solution is saturated. 

3. How many pounds of potassium chlorid in a ton 
of muriate of 80 per cent grade? 



Muriate of Potash 37 

4. How much potash is there in a ton of kainit 
containing 12 per cent K2O? 

5. If potassium chlorid and magnesium sulfate 
solutions are mixt what salt is most likely to be pre- 
cipitated? Why? 

6. What is the solubility of four salts used in the 
exercise? Express relatively at some definite tem- 
perature, putting the most soluble at the head of the 
colum. 

7. What materials, in addition to sodium chlorid, go 
to make up the 20% impurities in ordinary muriate 
of potash? 

8. How does the double sulfate of potash-magnesia 
decompose upon being dissolvd in a small quantity 
of water? 

9. What use is made industrially of the magnesium 
chlorid brine that, in this exercise, is thrown away after 
the high-grade muriate of potash has b3en filterd off? 

10. Deicriba the American sources of potash. 



LEAD NITRATE 

Lead nitrate is made from litharge, PbO, 
and nitric acid. 

Calculation. — From the equation, 

PbO + 2HNO3 = Pb(N03)2 + H2O, 

calculate the amount of nitric acid required 
to act on 20 grams of lead oxid. Read the 
spindle floating in the nitric acid to be used 
and, by reference to the table at the end of 
this exercise, ascertain how many grams of 
actual nitric acid in one cubic centimeter of 
this liquid. By division find out how many 
cubic centimeters of this nitric acid must 
be used. 

Enter the results in the following form : 

Nitric acid required, grams, 

Density of nitric acid solution, 

Number grams nitric acid in 1 cc, 

Volume of nitric acid solution, required, cc, 

Procedure. — Weigh out 20 grams of 
litharge, and place it in a small beaker with 
the required amount of nitric acid. Heat 
until the oxid is converted to nitrate and 
solution results, adding more water, if neces- 
sary, to dissolv the crystals of lead nitrate. 

38 



Lead Nitrate 39 

If a white precipitate of lead sulfate is pres- 
ent the mixture must be filterd to remove the 
lead sulfate. Heat the filtrate, or the clear 
solution, in case filtration was not necessary, 
until it is saturated; then either cool the 
solution rapidly or allow it to stand until the 
next exercise. The lead nitrate crystals may 
be filterd on an ordinary filter or on a Witt 
plate and dried in the open air. If the amount 
of mother-liquor (filtrate) is considerable 
more crystals may be obtaind by continuing 
the evaporation of the liquid. ^ 

NOTES V 

It is essential that the apparatus be 
clean. If sulfates are introduced by means 
of the measuring cylinders or beakers 
white insoluble lead sulfate will be formd 
which must be filterd out. If commercial 
nitric acid is used it may contain sulfuric apid. 

If the Htharge does not all dissolv more 
nitric acid may be added or the solution may 
be filterd and the excess litharge discarded. 
An excess of nitrate ions from the acid re- 
duces the solubility of the lead nitrate in 
water so it is difficult to use solubility tables 
to determin the least volume of hquid neces- 
sary to hold the amount of lead nitrate pro- 
duced in solution. 

The amount of lead nitrate in 100 cc. of a 



40 



Preparation of Substances 



solution saturated at given temperatures is 
found in the following table. 

Solubility Table 



Temperature 


0° 


10° 


18° 


25° 


50° 


100° 


Pb(N03)2grams 


36 


44 


51 


56 


79 


127 



Strength of Nitric Acid Solutions 





1 cc. contains 


Density. 


nitric acid, 




grams. 


1.05 


0.094 


1.10 


0.188 


1.15 


0.2177 


1.20 


0.388 


1.25 


0.486 


1.30 


0.617 


1.35 


0.753 


1.40 


0.914 


1.45 


1.121 



QUESTIONS 
(To be answerd in the notebook.) 

1. How many grams of lead nitrate could be made 
from 20 grams of litharge? What amount of boiling 
water is necessary to dissolv this amount of salt? 
(See solubility table.) 

2. How many grams of lead nitrate did you make? 

3. Is the salt more or less soluble in nitric acid than 
in water? Why? 

4. How many cubic centimeters of nitric acid of a 
density of 1.10 would be necessary to measure out if 
200 grams of actual acid were required? 

5. How is nitric acid made? Explain the presence 
of sulfuric acid in commercial nitric acid. 



LEAD ARSENATE 

Lead arsenate is the standard arsenical 
poison for chewing insects. It is made by 
mixing equivalent amounts of solutions of 
either lead acetate or lead nitrate with sodium 
arsenate. 

Calculation. — Inquire as to the character 
of the sodium arsenate available — as to its 
condition of hydration and degree of purity 
— and from the equation, 

Na^HAs04 • 7H2O + Pb(N03)2 = PbHAs04 
+ 2NaN03 + 7H2O, 

calculate the amount of disodium hydrogen 
arsenate that will be necessary to react with 
20 grams of lead nitrate. 

If the salt is hydrous the 7H2O will be weighd out 
and must be calculated; if anhydrous the 7H2O must 
be left out of the calculation. If the salt is 80 per cent 
pure the amount to be used must be increased by divid- 
ing by 0.80. 

Dissolv the lead nitrate in 50 cc. of warm 
water and dilute to a total volum of 350 cc. 
with cold water. Similarly dissolv the req- 
uisit amount of arsenate of soda in a little 
warm water and dilute to 350 cc. with cold 

41 



42 Preparation of Substances 

water. Mix the two solutions. Test the 
hquid with pieces of red and blue litmus 
paper. 

As the precipitate of white lead arsenate 
settles decant the clear supernatant liquid 
— best over the edge of the beaker, not using 
the lip — fill the beaker with fresh water, stir 
the mixture and again allow the precipitate to 
settle. Repeat this washing until the soluble 
salts are removed, and the precipitate, be- 
coming colloidal in character and refusing to 
settle completely, is partially dispersed thru 
the liquid. 

This condition being reacht allow the mix- 
ture to stand over night, so that as much as 
possible of the lead arsenate will settle out, 
then decant most of the Uquid, neglecting the 
loss of the comparatively small amount of 
precipitate in colloidal condition, and bring 
all the remaining precipitate gradually onto 
one 15-cm. filter folded in the ordinary way. 
Allow the precipitate to drain in the funnel 
for several days; even a week, as a rule, is 
not too long. 

When the amount of moisture is reduced 
to about 50 per cent the mass will separate 
easily from the paper and should be handed 
in. 



Lead Arsenate 43 



NOTES 



With large beakers such as are most al- 
ways used in this washing process it is an 
easy matter to put a stirring rod thru the 
bottom or sides of the beaker. The student 
should learn to stir without touching the 
stirring rod to the beaker. In such a case as 
the one in hand the stirring is best done by 
the force of the entering wash water. 

The quality of the sodium arsenate on the 
market varies greatly. The best grades are 
crystallin and hydrated. The inferior grades 
are frequently anhydrous, massiv, of spongy 
appearance and carry considerable sodium 
carbonate and sulfate. 

If the two salts are not used in equivalent 
proportions the litmus paper will show which 
was taken in excess. Lead nitrate turns the 
paper red while sodium arsenate turns it 
blue. 

The washing takes out the excess of either 
salt that may have been used, and the sodium 
nitrate formd by the reaction. In the pres- 
ence of any considerable quantity of these 
salts the small particles of lead arsenate are 
flocculated, that is, many thousands are 
brot together in one floe. As the concen- 
tration of the soluble salts is lowerd by wash- 
ing the particles separate, are deflocculated, 



44 Preparation of Substances 

'and become so small that their rapid motion 
ofsets the force of gravity. 

The rapid motion of any small particle 
in suspension may be easily observd under 
a high power microscope. The motion is 
produced by the molecules of water which 
strike the larger particles with sufficient force 
and frequency to keep them in oscillation. 
This motion is known as the " Brownian 
movement.^' 

The action which the arsenate of lead 
undergoes in becoming colloidal is said to 
be as follows: When the soluble salts (elec- 
trolytes) are sufficiently decreased by the 
washing process some groups of mole- 
cules of lead arsenate react with either the 
hydrogen or the hydroxyl-ions of the water 
combining with them. If the particles com- 
bine with the hydrogen they become posi- 
tively charged colloids and the Uquid re- 
taining the negativ hydroxyl group becomes 
negativ. It is entirely possible that it is 
the layer of atoms on the , surfaces of the 
particles of arsenate of lead which is active 
in combining with either the H"*" or the ~0H 
of the water. The action of salt in coagu- 
lation, or precipitation, consists in neutraliz- 
ing the electrical charges. As this takes 
place the lead arsenate particles, which were 
previously all of the same electrical condi- 



Lead Arsenate 45 

tion and consequently were all repellent of 
each other, gradually floe together, the 
Brownian motion slows down, and as the 
particles continue to coalesce the Brownian 
motion ceases and the solid separates out as 
a precipitate. 

The arsenate of lead formd is a mixture of 
two compounds; one acidic having the sym- 
bol PbHAs04, and one basic represented by 
the formula Pb3As204 • Pb20HAs04. These 
two compounds are in equiUbrium, 

5PbHAs04 + HOH ^ Pb50H(As04)3 
+ 2H3ASO4, 

the acidic one being gradually changed to the 
basic one as the arsenic acid formd in the 
reaction is decanted off during the washings. 
The change to the basic compound, however, 
is very slow as with very slight concentra- 
tions of arsenic acid such as accumulate in 
the wash water the action stops and no more 
basic compound is formd until the superna- 
tant wash water is replaced by fresh. As an 
example of the slowness of the change it 
required, in an experiment by McDonnell 
and Graham of Washington, D. C, con- 
tinuous washing for a year to change two 
grams of the lead acid arsenate to the basic 
substance. 

A piece of blue litmus paper added to the 



46 Preparation of Substances 

mixture after the material has been well 
washt will turn red slowly showing the pres- 
ence of a slight concentration of acid. This 
is the arsenic acid hydrolyzed off from the 
acid arsenate. 

The addition of any acid changes the 
equilibrium from right to left forming the 
acidic arsenate with the elimination of the 
basic compound. Most of the lead arsenate 
pastes on the market are made with lead 
nitrate and the acidity of the system is 
sufficient to produce a mixture consisting 
mostly of the acid arsenate with smaller 
proportions of the basic compound. 

Inasmuch as the acidic arsenate consists 
of approximately 33 per cent AS2O5 and the 
basic approximately 23 per cent the analysis 
of the compound will show the proportions 
of the two arsenates present. For example, 
a mixture of the two analyzing 30 per cent 
AS2O5 is nearly all acidic and contains very 
Uttle of the basic compound, while one 
analyzing 28 per cent is composed of equal 
parts of the two arsenates, basic and acidic. 
These facts can be applied to the analysis of 
two commercial samples of arsenate of lead 
which are here given, one made from, lead 
nitrate which contains a strong acid and the 
other made from lead acetate containing a 
weak acid. 



Lead Arsenate 



47 



Analyses of Lead Arsenate 





Made from lead 

nitrate, per cent in 

dry salt. 


Made from lead 

acetate, per cent in 

dry salt. 


AsoOo. . . . 
PbO 


31.40 

62.80 


25.40 
74.11 



It will be seen that both preparations are 
mixtures of the two compounds, the one made 
from lead nitrate containing much more, in 
fact is nearly all, of the acidic compound 
PbHAs04, while the one made in the presence 
of less acid contains a large proportion of the 
basic compound. 

Most of the arsenate of lead on the market 
is in the form of a paste containing 45 to 50 
per cent water, consequently the actual per 
cents of arsenic and lead oxids in the ma- 
terials would be about one-half the figures 
just given. The dry powder on the market 
is said to be made by an entirely different 
process, by suspending lead plates in arsenic 
acid and causing chemical action by means of 
an electric current. The lead arsenate that 
falls off the plates has only to be washt and 
dried. 

For most uses lead arsenate replaced Paris 
green as an arsenical poison. Its two advan- 
tages are its greater insolubility and its abihty 
to stick. The solubility of lead arsenate in 



48 Preparation of Substances 

pure water is extremely slight. It is, how- 
ever, readily decomposed by the salts which 
appear in natural waters, the carbon dioxid of 
hard water being particularly effective. The 
amounts of arsenic acid set free by this reac- 
tion are, generally, less than one per cent, 
depending on the water used and not enuf to 
burn foliage. 

QUESTIONS 
(To be answerd in the notebook.) 

1. How many grams of anhydrous, 80 per cent 
pure, arsenate of soda would be required to put with 
20 grams of lead nitrate? 

2. Explain how lead nitrate can turn litmus red. 

3. Similarly, how sodium arsenate can turn litmus 
blue. 

4. What is meant by the terms flocculent; de- 
flocculated? 

5. Explain the action of soluble salts in flocculating 
the precipitate. 

6. What salts are washt out of the mixture? How 
did the Utmus paper act in your preparation im- 
mediately after mixing? 

7. How much arsenic acid (AS2O5) in an ordinary 
lead arsenate paste? 

8. If lead costs more than arsenic which is cheaper 
to use as a lead salt, the nitrate or the acetate? The 
analyses of lead arsenates given v\dll furnish the answer. 

9. Calculate the per cents of AsoOs and PbO in 
PbHAs04 in the basic compound. This will be confus- 
ing unless the student keeps in mind the fact that the 
amount of two arsenics cannot be calculated where 
only one exists, i.e., AS2O5 cannot be calculated from 



Lead Arsenate 49 

one molecule PbHAs04, whereas it can from two mole- 
cules. In other words the student is askt to resolv 
2PbHAs04 into 2PbO, AsoOs and H2O, the water being 
neglected in this case. 

10. What are the advantages of lead arsenate over 
Paris green? 



LIME-SULFUR 

36-80-50 Fonnula 

Lime-sulfur is an amber colord liquid con- 
taining calcium polysulfids, CaS4 and CaSs, 
and some calcium thiosulfate, CaS203. It is 
made by boiling lime with a suspension of 
sulfur. It first came into use as an insecticide 
on the Pacific coast about 1900 to combat the 
San Jose scale. Previous to that time a 
''Lime, Sulfur and Salt" mixture had been 
used as a sheep wash. Nowadays its use in 
more dilute solutions is extending rapidly to 
control ''blights" or fungus diseases, while 
the stronger solution is still one of the stand- 
ard remedies for scale insects. In the 
stronger solutions it is appl'ed during the late 
winter or early spring before the buds burst. 

Procedure. — Select a beaker or porcelain 
dish of 400-500 cc. capacity, measiu-e into it 
200 cc. of water, and mark the level of the 
Hquid so that the mark can be recognized 
after the dish is used for bo' ling. Weigh out 
38 grams of quicklime, and slake it in the 
proper amount of water. Weigh out 80 
grams of sulfur flour and make this into a 
thoroly moistend paste with about 200 cc. of 

50 



Lime-Sulfur 51 

water. Bring the ingredients together in 
the markt dish, place the dish on a piece of 
asbestos over a flame, and keep the mixture 
boiUng gently. 

Dm-ing the boihng replace the water if it 
gets near the 200 cc. mark. It is not neces- 
sary that any particular volum should re- 
main at the end of the boiling period; the 
less water the stronger the solution and the 
more thiosulf ate is decomposed and the more 
CaSs is formd in place of CaS4; however, if 
the solution is made too concentrated there 
will not be sufficient Hquid to float the 
hydrometer spindle. To make a solution of 
the same density as the commercial prepara- 
tions, 34° Be., it would be necessary to con- 
centrate the liquid to less than 200 cc. 

When the liquid acquires a dark amber 
color and the suspended sulfur has dis- 
appeard the lime-sulfur is made. This may 
require an hour. If the preparation is to 
stand until the next exercise it should be 
coverd to keep out as much oxygen as pos- 
sible. Reducing the surface by placing the 
mixture in a narrow vessel also reduces the 
oxygen absorption. If it is intended to com- 
plete the work at once the mixture may be 
coold by immersing the container in water. 
After standing observe that a crust has 
formd on the surface of the hquid which is 



52 Preparation of Substances 

much thicker if the preparation has stood 
for several days. Decant the clear hquid 
into the special lime-sulfur hydrometer cyl- 
inders and take the density on both the 
specific gravity and Beaume scales. From 
the concentrated clear liquid prepare two 
sprays, one for use when the buds are dor- 
mant and one for use on the green foliage 
in summer. Take the density (Be.) of both 
diluted sprays and record the data in the 
notebook. 

If any lead arsenate is available make a 
thin paste of this and add some of it to the 
dilute summer spray. Notice the gradual 
darkening as some of the lead is withdrawn 
from the combination with arsenic acid and 
combined with sulfur to form black lead 
sulfid; small amounts of arsenic acid are set 
free at the same time. This is a combination 
spray having two functions, insecticidal and 
fungicidal. 

NOTES 

The 1910 Geneva Formula, 36 pounds 
of lime; 80 pounds sulfur; 50 gallons water, 
is here made over for laboratory use. The 
directions are based on bulletin No. 329 
of the New York Agricultural Experiment 
Station, by Van Slyke, Bosworth and Hedges. 

If the lime is pure 36 grams should be used, 
if 95 per cent CaO (i.e., 5 per cent MgO) 



Lime-Sulfur 53 

38 grams should be used, if 90 per cent lime 
40 grams. Lime that is over 10 per cent 
magnesium oxid should not be used as 
it is a waste of material. The magnesium 
forms insoluble compounds that go into the 
sediment. In case the lime is already slaked 
increase the quantity in the ratio of the 
weights of CaO : CaOaHa {i.e., 56 : 74). 

It is an easy matter to select lime that 
carries less than 2 per cent of magnesia as the 
analysis is on the barrel and the product of a 
given lime-kiln is fairly constant in compo- 
sition. 

If all the material is not in very finely 
divided condition it will remain as sediment 
and not react; hence the sulfur is moistend 
to prevent lumping. 

If a beaker is used place a piece of asbestos 
under it, otherwise the solid material will 
form a blanket over the bottom of the beaker 
and prevent the diffusion of the heat. The 
glass will not stand sudden local heating and 
cooling resulting from such blanketing. 

The reactions which take place when the 
material is being made, according to Pro- 
fessor Tartar at the Oregon Agricultural Ex- 
periment Station, are, first, the action of lime 
and sulfur to form calcium tetrasulfid, and 
calcium thiosulfate, 

3Ca02H2 + lOS = 2CaS4 + CaS203 + 3H2O. 



54 Preparation of Substances 

Second, as the liquid becomes concentrated 
the calcium thiosulfate breaks down forming 
the insoluble calcium sulfite liberating one 
atom of sulfur, 

CaS203 = CaSOa -f- S. 

This reaction may be taking place in this 
experiment when the volume of the liquid is 
reduced to about 200 cc. The insoluble cal- 
cium sulfite remains as a sediment. Third, 
the sulfur liberated from the thiosulfate unites 
with the tetrasulfid forming pentasulfid, 

CaS4 -i- S = CaS5. 

Thus the composition of the mixture 
changes during concentration. The amounts 
of thiosulfate and tetrasulfid become lessend 
and the quantity of pentasulfid increased. 
Such changes are considerd desirable and 
have been effected in most of the commercial 
preparations on the market. 

Combination sprays may be made by mix- 
ing Hme-sulfur with arsenate of lead or 
nicotine sulfate, or both, and simultaneously 
kill chewing insects and aphis, as well as 
prevent attacks of fungus diseases. 

Professor Schaefer, of the Michigan Agri- 
cultural College, states that the action of 
lime-sulfur solution upon the San Jose scale 
is one of suffocation; that the caustic liquid 



Lime-Sulfur 55 

finds its way under the edges of the httle 
shell under which the insect lives, shutting 
off the outside oxygen and rapidly con- 
suming what remains inside. 

The fungicidal action of lime-sulfur is 
thot to be due to the sulfur deposited from it. 
This, in the air, oxidizes slowly to sulfur 
dioxid which is toxic. 

Long boihng exposed to the air, as is neces- 
sary in laboratory manipulation, is harmful 
to the product as the polysulfids react rapidly 
with the oxygen of the air depositing sulfur 
and forming thiosulfate, 

CaSa + 30 = CaSaOa + 3S. 

This is the change that takes place when 
lime-sulfur stands exposed to the air. At 
first only a film of sulfur is seen as the cal- 
cium thiosulfate dissolvs, but as the upper 
layer becomes saturated with* thiosulfate 
crystals these become mixt with the sulfur 
forming a hard crust. It is evident from this 
that the mixture should not stand in the 
laboratory any longer than necessary. 

The action of lime-sulfur when used as a 
spray follows from the explanation in the 
previous paragraf. First, it rapidly takes 
up oxygen forming calcium thiosulfate and 
depositing all the sulfur in excess of two atoms 
to the molecule. Second, the thiosulfate 



56 



Preparation of Substances 



slowly breaks down to insoluble sulfid and 
one atom of sulfur is set free. This change 
is slow and is represented by the equation, 

CaS203 = CaSOs + S. 



Lime-Sulfur Table * 
Data furnishing a basis for diluting lime-sulfur wash 













Dilution as indicated for 












Iga 


. solution. 




Sulfur 

to 
1°B6., 


Sulfur 

in sol., 

per 


VVt. one 
gal., 
lbs. 


Sulfur 

in one 

gal., 








Den- 
sity. 


Dormant 


Blister 


Sum- 




per 
cent. 


cent. 


lbs. 


(San Jo.se 


ndie, 
gals. 


mer 

spray, 












scale), 


gals. 












^als. water. 




water. 


36 


0.75 


27.00 


11.08 


2.99 


9 


121 


45 


35 


0.75 


26.25 


10.98 


2.88 


8f 


12 


43i 


34 


0.75 


25.50 


10.88 


2.77 


81 


111 


4U 


33 


0.75 


24.75 


10.78 


2.67 


8 


11 


40 


32 


0.74 


23.70 


10.69 


2.53 


7h 


101 


371 


31 


0.74 


22.95 


10.60 


2.43 


71 


10 


361 


30 


0.73 


21.90 


10.51 


2.30 


61 


9i 


m 


29 


0.73 


21.15 


10.42 


2.20 


61 


9 


32| 


28 


0.72 


20.15 


10.32 


2.08 


6 


81 


31 


27 


0.72 


19.45 


1J.23 


1.99 


5f 


8 


29i 


26 


0.71 


18.45 


10.15 


1.87 


51 


71 


27f 


25 


0.70 


17.50 


10.07 


1.76 


5 


7 


26 


24 


0.69 


16.65 


9.98 


1.65 


41 


61 


24i 


23 


0.68 


15.65 


9.90 


1.55 


41 


6 


22f 


22 


0.67 


14.75 


9.82 


1.45 


3i 


51 


2U 


21 


0.66 


13.85 


9.74 


1.35 


3i 


5 


191 


20 


0.65 


13.00 


9.67 


1.26 


3^ 


41 


m 


19 


0.65 


12.35 


9.59 


1.18 


3 


4i 


17 


18 


0.65 


11.70 


9.51 


1.11 


21 


4 


16 


17 


0.65 


11.05 


9.44 


1.04 


21 


3f 


15 


16 


0.65 


10.40 


9.37 


0.97 


2i 


3| 


14 


15 


0.65 


9.75 


9.30 


0.90 


2 


3 


121 



* From Bulletin No. 329, page 316, New York Agri- 
cultural Experiment Station; Van Slyke, Bosworth and 
Hedges. 



Lime-Sulfur 57 

Third, the sulfite takes up oxygen forming 
calcium sulfate, 

CaSOa + O = CaS04, 

so that calcium sulfate and sulfur are the 
final products of decomposition of the lime- 
sulfur mixture. 

The analysis of a commercial lime-sulfur 
concentrate is as follows: 

Sp. gr., 1.30 or 33.7 B6. 

Sulfur in thiosulfate, 0.25% 

Sulfur in tetrasulfid, 0. 50% 

Sulfur in pentasulfid, 24 . 75% 

Total sulfur, 25.50% 

This shows that the amount of thiosulfate 
has been greatly reduced, and that the sub- 
stance present in greatest quantity is cal- 
cium pentasulfid. 

QUESTIONS 
(To be answerd in the notebook.) 

1. Did you have sufficient lime-sulfur solution to 
float the hydrometer spindle? What was the Beaume 
reading of your solution? 

2. How many pounds of sulfur in one gallon of your 
solution? 

3. How much would the sulfur in 50 gallons cost 
at the rate of $20.00 per ton? 

4. What dilution did you make for the San Jose 
scale? What was the density of the dilute solution? 



58 Preparation of Substances 

5. What dilution for summer spray? Resulting 
density? 

6. What change was observd when lead arsenate 
was mixt with the summer spray? What new in- 
soluble substance was formd? 

7. What is the per cent of sulfur in the lime-sulfur 
you made? 

8. What substances are in lime-sulfur? Under- 
score the one present in largest quantity. 

9. What is in the sediment in lime-sulfur? 

10. Write the reactions that take place when the 
lime-sulfur is made, placing the name of each substance 
imder its symbol. 

11. Similarly write the series of reactions that take 
place when lime-sulfur is oxidized. 

12. What effect on the composition of lime-sulfur 
has long boiling? The concentration below 200 cc? 

13. What are the uses of lime-sulfur? 

14. What is said ta be the action of lime-sulfur 
in killing San Jose scale? 

15. What are the final products of oxidation of 
lime-suKur? 

16. A barrel of lime-suKur was left half full over one 
season. What substances would be found in the 
crust that formd on the liquid? 

17. What specific gravity is equivalent to 33 B6.? 

18. What are the ordinary impurities in lime? 

19. Write the reaction for slaking lime. 

20. How many grams of slaked lime can be made 
from 40 grams of quicklime? 



COPPER SULFATE 

Procedure. — Place in a beaker 10 grams 
of metallic copper, 50 cc. of water, 15 to 18 cc. 
of chamber sulfm-ic acid and 25 cc. of dilute 
(sp. gr. 1.2, 32 per cent) nitric acid. Place 
the mixture on asbestos, under a hood, and 
heat gently with a low flame until the copper 
is all dissolvd. This should require about 
an hour. In case the solution becomes 
saturated during the heating as evinst by 
the crystals forming on the surface, add a 
few drops of water. When the copper is all 
dissolvd continue heating until the solution is 
saturated, then remove the beaker, place it 
in cold water and stir the solution as it cools 
until crystallization is complete. Filter off 
the crystals on a Witt plate. Evaporate 
the filtrate to the point of crystallization and 
cool the liquid until all the crystals have 
formd that will. If possible pour out the 
mother liquor, which consists mostly of strong 
acids, and bring the remaining crystals onto 
a Witt filter. Put both crops of crystals into 
25 cc. of boiling water and adjust the quan- 
tity of water, by adding directly and boiling 
off, until the salt is all dissolvd and the solu- 

59 



60 Preparation of Substances 

tion becomes saturated. Cool the liquid 
with stirring or allow it to stand until the 
next exercise. Filter off the crystals and dry 
them between filter paper. Save the mother 
liquor for the tests which follow. 

Tests for copper ; Notebook. — Test some 
copper sulfate by adding ammonium hy- 
droxid, at first one drop, then in larger quan- 
tity. The light blue insoluble substance 
f ormd by the small amount of ammonia is a 
basic copper sulfate; the blue solution con- 
tains copper and ammonia together in one 
ion, an ammonio-cupric sulfate Cu(NH3)4S04. 
This solution contains very few copper ions — 
only those that break away from this com- 
plex. The formation of a blue solution is a 
test for copper. To the blue solution add a 
few drops of potassium ferrocyanide. There 
being so few Cu ions the copper ferrocyanide 
formd is not v sible. Break up the ammonio- 
copper complex by adding acetic or dilute 
hydrochloric acids. As soon as copper ions 
are present in amount of about 0.002 per cent 
the copper ferrocyanide begins to be visible. 

Add a few drops of potassium ferrocyanide 
to a copper sulfate solution. The formation 
of brown copper ferrocyanide is a test for 
copper. 



Copper Sulfate 61 

NOTES 

Bluestone or copper sulfate is the impor- 
tant salt of copper for agriculture. Its weak 
solution is fungicide and a disinfectant. 
Seed wheat is treated with it to kill the 
spores of the smut. Bordeaux mixture and 
Paris green are made from it. 

Copper does not dissolv in acids without 
first being oxidized. This may be accom- 
pUsht, superficially, by heating in air when 
the resulting coating of black copper oxid 
will dissolv in sulfuric acid. Copper may be 
fused with sulfur when the resulting copper 
sulfid will respond to the action of sulfuric 
acid. The unreduced copper sulfid of copper 
matte which falls to the bottom of the tank 
when crude copper is electrolytically purified 
is used to make copper sulfate. Copper 
moistend with acid will take oxygen from the 
air and dissolv slowly. In this experiment 
the oxygen is obtaind from nitric acid. 

QUESTIONS 
(To be answerd in the notebook.) 

1. From the sjnnbol, CUSO4 • 5H2O, calculate the 
amount of crystallized salt that may be made from 10 
grams of metallic copper. 

2. From the same sjrmbol find out how many grams 
of suKuric acid would be necessary. 

3. Consult the table of the density of suKuric acid 
imder superphosphate and determin how many cubic 



62 Preparation of Substances 

centimeters of sulfuric acid would be necessary to 
contain the number of grams found under 2. 

4. What volum of nitrogen oxids was given off in 
tliis experiment? "To solv this problem it will be 
necessary to establish the relationship between the 
weight of copper used and the volum of gas given off. 
The gas given off is the colorless nitric oxid which 
changes to the brown nitrogen dioxid without change 
in volum upon exposure to the air. The following 
equation shows the decomposition of nitric acid as it 
takes place in the experiment, 

4HNO3 = 2H2O + 3O2 + 4N0. 

The change from the colorless to the brown oxid is 
simple, 

2N0 +02= 2NO2, 

and the quantities 2N0 and 2NO2 bear out the state- 
ment that there is no change in volum in the oxida- 
tion of nitric oxid to nitrogen dioxid. The relation of 
the nitrogen dioxid to the copper must be sought thru 
the oxygen which unites with the copper, 

Cu + = CuO. 

The copper being once oxidized we lose interest in it, 
for the purposes of this calculation, as it reacts with 
the sulfuric acid without changing its relationship to 
the oxygen, 

CuO + H2SO4 • aq. = CUSO4 • aq. 

Now it is possible to establish the relationship of the 
copper to the nitrogen dioxid thru the oxygen as fol- 
lows: One Cu unites with one 0, hence 6Cu unites 
with 3O2 and, from the first equation, the produc- 
tion of 3O2 is accompanied by the evolution of 4N0 
which goes to 4NO2 without change in volum. Then 
6Cu are accompanied by the production of 4NO2 



Copper Sulfate 63 

which establishes the relationship between the copper 
and the gas given off. The number of giams repre- 
sented by the symbol NO2 occupies 22.4 Hters (molec- 
ular volum). Now we have the complete data for the 
ratio which is 

6Cu _ 381.6 grams of copper 

4(22.4 liters) 89.6 hters of gas 

As 10 grams of copper were used in the experiment the 
following proportion will give the number of hters of 
gas produced: 

?^ = 15 = Uters of either NO or NO2. 
89.6 X 

5. What is necessary to make copper dissolv in 
acids? 

6. What are the uses of copper sulfate? 

7. What are two tests for copper? What compound 
in each case is used to recognize the copper? 

8. How can the number of copper ions in a solution 
be reduced to a negUgible quantity? 

9. What oxid, or oxids, of nitrogen are red? What 
colorless? 

10. How many liters of nitrogen dioxid were given 
off in this experiment? Of nitric oxid oxidized by the 
air? How many grams of each? 



PARIS GREEN 

Paris green closely approximates the for- 
mula Cu(C2H302)2 • 3Cu(As02)2, which was 
assignd it by Ehrmann in 1834, and is cald 
an aceto-arsenite of copper. There are two 
general processes for making it, first replacing 
most of the acetate ion of copper acetate by 
the arsenite ion of arsenious acid ; and second, 
replacing some of the arsenite ion of copper 
arsenite by the acetate ion of acetic acid. 
The latter process is foUowd in these direc- 
tions. 

Procedure. — Dissolv 9 grams of dry 
carbonate of soda, or 24 grams of hydrous, in 
a beaker or porcelain d'sh in 80 cc. of water. 
Into this solution sprinkle gradually 16 
grams of arsenious oxid, and boil until the 
acid has united with the soda as shown by 
solution of the resulting sodium arsenite. 

Dissolv 20 grams of copper sulfate in 80 
cc. of water. When both of the solutions 
are at about 60° — as warm as the hand can 
comfortably bear — pour the sodium arsenite 
solution into the copper sulfate. Add 10.5 
cc. of 50 per cent acetic acid — or an equiva- 
lent of any other strength, and allow the 

64 



Paris Green 65 

mixture to digest at about 50° for some time 
on a piece of asbestos board over a low flame. 
If the green copper aceto-arsenite does not 
form at this point, not enough acetic acid 
has been added. Consult an Instructor 
before adding more than a few drops of acid 
as too much may decompose the salt. Stir 
occasionally — once in five minutes — and 
when the reaction seems complete drain the 
green product on a funnel and wash to 
remove soluble arsenites and sodium sulfate. 
Examin the size and shape of the particles 
under a microscope. When dry put in a 
clean, dry beaker and see if it ''flows" well. 

NOTES 

Paris green is one of the oldest arsenical 
insecticides. For many years it was the 
standard remedy for the potato beetle. It 
is applied to the vines suspended in water. 

The composition of Paris green required 
by the symbol is never exactly attaind, the 
amount of arsenic being somewhat less than 
the ideal quantity. The analysis of a theo- 
retical compound of the formula given, of 
two samples of Paris green carefully made, 
and the average analysis of 494 samples 
bot on the open market in Pennsylvania, are 
given in the following table: 



66 



Preparation of Substances 



Analyses of Paris Green 





Theoretical, 


Avery, 
Nebraska. 


Holland 
and Reed, 
Massachu- 
setts. 


Ke'.!o2. 
average 494 

samples, 
Penn., 1910. 


AS203 

CaO 

(CH3)2(CO)20 

H20 


58.55 
31.39 
10.06 


57.55 
31.75 
10.31 


56.94 

31.74 

10.37 

78 


57.97 

29.41 




100.00 


99.61 


99.83 









It is noticed that while the arsenic falls 
about one per cent short the amount of copper 
oxid is slightly increased as is the acetic a(iid, 
this may be taken to mean that there is 
slightly more copper acetate in the compound 
than is shown by the symbol. 

In the solution from which Paris green is 
made, arsenite, acetate and copper ions must 
be in such concentrations, and the tempera- 
tures so adjusted as to allow the formation 
of the copper aceto-arsenite. Too much 
acetic acid will throw the white arsenious oxid 
out of solution. The reagents must be 
measured with considerable care to avoid the 
effect of varying masses. The base and acids 
concernd are all weak, and the compound is 
easily hydrolyzed by water; hence the long 
digestion to allow the formation of large 
particles in which the ratio of mass to surface, 
m/s, is greater. 



Paris Green 67 

QUESTIONS 
(To be answerd in the notebook.) 

1. Name the acidic and basic ions used in making 
Paris green. 

2. What shaped particle has the largest ratio of m/s? 

3. What are the relativ advantages of Paris greens 
composed of large particles; of small particles; of 
particles of spherical shape; of broken cornered par- 
ticles? (Discuss in reference to degree of hydrolysis 
and time of suspension.) 

4. What is the objection to putting Paris green in 
water several days before using? Of applying on a wet 
day? 

5. How many grams of crystallized sodium carbon- 
ate, Na2C03 '101120, could be made from 10 grams of 
the anhydrous salt? 

6. Water hydrolyzes Paris green. State some of 
the possible products of hydrolysis. Which of these 
are soluble? 

7. Write a s^ymbol for orthoarsenious acid; meta- 
arsenious acid. (See textbook.) 

8. Write a reaction between Na2C03 and AS2O3 
naming all the substances. 

9. Write the symbol of acetic acid. 

10. How many grams of arsenic trioxid will react 
with 24 grams of dry sodium carbonate? 



BORDEAUX MIXTURE 

I. ORDINARY BORDEAUX 

The composition of the mixture produced 
by the formula ordinarily used, 4-4-50, is 
said to be a basic sulfate of copper and hme; 
its composition being represented by the 
symbol, CuS04-9CuO.CaS04-3CaO. 

Procedure. — Weigh out 8 grams of cop- 
per sulfate, dissolv it in 50 cc. of water, using 
heat if it is desired to hasten the solution, and 
add 350 cc. of cold water making the total 
volum 400 cc. Slake 8 grams of quicklime 
with a little water, dilute the paste with about 
200 cc. of cold water and strain the mass thru 
a piece of cheesecloth placed over a funnel 
or a thistle tube. Dilute the milk of lime to 
400 cc. Mix the cold solutions. 

n. WOBURN BORDEAUX 

Woburn Bordeaux may consist of either 
of three basic sulfates of copper, the pro- 
portions of base to acid in each being shown 
in the following formulas: CuS04*3CuO; or 
CuS044CuO; or CuS04-9CuO.CaS04. Its 
most striking characteristic is the absence 
of any free lime. Either of the three com- 

68 



Bordeaux Mixture 69 

pounds may be made in this experiment ac- 
cording to the amount of hme-water used. 

Procedure. — Weigh out 0.5 gram of 
copper sulfate or get a solution containing 
that amount and dilute it to 380 cc. Meas- 
ure out either 70, 74 or 84 cc. of lime-water 
and dilute it to 380 cc. Mix the two solu- 
tions. 

Properties of Bordeaux Mixtures; Note- 
book. 

1. Compare the color of the two mixtures. 

2. Stir them up and allow to stand. Which stays 
in suspension best? 

3. How much does each mixture settle in 15 min- 
utes? Is a white scum to be seen on either prepara- 
tion? If so which one? 

4. Filter some of the Woburn Bordeaux and add 
a few drops of potassium ferrocyanide solution to test 
tube of the clear filtrate. If copper is in solution as 
positiv ion, in amounts of over 0.002 per cent, the 
brownish color of copper ferrocyanid should be seen. 
It may be necessary to look down the colum onto a 
white background to see the color and it may be well 
to compare this tube with another containing only 
water and the same number of drops of ferrocyanid 
solution. Are any copper ions (Cu++) in solution? 

NOTES 

The ordinary, or one per cent, Bordeaux 
is made from 4 pounds of copper sulfate, 
4 pounds of quicklime and 50 gallons 
of water. This formula is here reproduced 



70 Preparation of Substances 

en a small scale suitable for laboratory pur- 
poses. The Woburn Bordeaux, if enlarged 
to barrel proportions, would consist of 4|- 
ounces of copper sulfate, 4|- gallons of lime- 
water in 51 gallons of the mixture. 

Several compounds of copper can be made 
by mixing lime and copper sulfate in different 
amounts. The following symbols* show the 
proportions present in the various substances 
that can be formd: 

(I) CuS04-3CuO. (II) CuS044CuO. 
(Ill) CuS04.9CuO.CaS04. (IV) CUSO4. 
9CuO.CaS04-3CaO. (V) CuO-SCaO. 

It will be noted that the compound (II) is 
more basic than (I) and that the basicity 
increases progressively so that (V) is all base. 
The compounds are produced successively, 
by using increased quantities of lime-water 
with the same amount of copper sulfate. 
For example, with 0.5 gram of copper sulfate, 
70 cc. of lime-water will produce the com- 
pound CuS04-3CuO, 74.1 cc. of lime-water 
will give CuS044CuO and 83.3 cc. of lime- 
water will make CuS04-9CuO.CaS04. Wo- 
burn Bordeaux may be any one of these 

* Taken from the 11th Annual Report (p. 25) of the 
Woburn Experimental Fruit Farm by the Duke of Bed- 
ford and Mr. Pickering. Some calcium sulfate is reported 
united with the first three compounds in addition to that 
represented. 



Bordeaux Mixture 71 

compounds or mrxtures of them. With a 
large excess of the base the compound 
(IV) is produced having the formula 
CuSO4.9CuO.CaSO4.3CaO. This is stiU 
more basic in that it contains some of the 
basic calcium sulfate in addition to the basic 
copper sulfate. Such a compound the ordi- 
nary Bordeaux mixture is said to be. 

From the symbol of the copper compound 
in ordinary Bordeaux, CuS04.9CuO.CaS04. 
3CaO, an equation may be written to account 
for the formation of such a substance, 

IOCUSO4 + 12Ca02H2 = CUSO4.9CUO. 
CaS04.3CaO + 8CaS04 + I2H2O. 

From this it is seen that considerable cal- 
cium sulfate is formd at the time the Bor- 
deaux is made. Calcium sulfate is soluble 
in water at 25°, to the amount of 0.21 gram 
per liter. If any free lime is left over, which 
is always the case, the solubihty is lessend, 
as both compounds contain a common cal- 
cium ion. 

A rough calculation on the part of the 
student will show that 8 grams of copper 
sulfate require about 2 grams of lime to 
react with it. For example, the formula for 
the precipitate in ordinary Bordeaux is 
given as CuSO4.9CuO.CaSO4.3CaO. Lime is 
used to produce the 9CuO and the 3CaO 



72 Preparation of Substances 

making 12CaO used for every lOCu; or 
more in detail, 9Ca02H2 were necessary to 
react with 9CuS04 before the resulting 
9CUO2H2 could form 9CuO and 3CaO are 
found in the product making a total of 12CaO 
required. The lOCu come from 10CuSO4- 
5H2O and thus the ratio between copper 
sulfate and hme, 10CuSO4-5H2O/12CaO, is 
establisht. In figures it is 2497.3/672 or 
3.7 showing that nearly four times as much 
Ume is used as is cald for by the symbol. 
This ratio has been fixt by horticultural 
practise. 

From the previous paragraf it is evident 
that nearly four times as much hme is used 
as is needed. The student will inquire as to 
what becomes of the remainder. The solu- 
bihty of calcium hydroxid at 25° is 0.16 
gram in 100 cc. of water. This amount, 
however, is lessend by the presence of cal- 
cium sulfate so that only a small portion of 
the whole amount of lime dissolvs in water. 
Further, not all the lime weighd out gets 
into the preparation, as lumps, air-slaked 
material and frequently lime itself may be 
rejected by the strainer. It is obvious that 
all the lime not in solution must be mixt in 
with the precipitate. 

The white scum is calcium carbonate 
made up of carbon dioxid from the air and 



Bordeaux Mixture 73 

the excess lime in solution. There must be 
lime enuf present to precipitate all the cop- 
per before there can be any left over to 
react with carbon dioxid so that the forma- 
tion of a white scum is proof that no copper 
remains in solution and that the mixture 
does not contain any soluble copper that can 
burn foliage. 

Bordeaux mixture protects plants from 
attacks of fungous diseases. When spread 
over the leaf it dissolvs very slightly and 
disease spores blown on by the wind are 
kild upon germination by the soluble copper 
formd. 

The substances which act upon the Bor- 
deaux to make the copper soluble, to the best 
of our present knowledge, are the carbon 
dioxid, the ammonia and the nitric acid 
present in the atmosphere. The carbon 
dioxid first combines with lime forming in- 
soluble calcium carbonate and following this 
begins the conversion of the copper to basic 
copper carbonate which is accompanied by 
the liberation of copper sulfate. Basic cop- 
per carbonate is dissolvd by more carbon 
dioxid, by ammonia, by nitric acid, or by 
ammonium nitrate made from the ammonia 
and nitric acid. The amount of soluble cop- 
per produced by the atmospheric agencies 
is very small, — thousandths or ten-thou- 



74 Preparation of Substances 

sandths of one per cent, — while the amount 
of soluble copper that a leaf can stand without 
burning is much larger and is in the neigh- 
borhood of 0.04 per cent. 

The ordinary Bordeaux mixture — con- 
taining four times as much ime as is needed 
for producing the insoluble copper compounds 
— after being spread out on the plant does 
not begin the liberation of soluble copper until 
the carbon dioxid of the atmosphere has 
acted on the excess of lime present. This 
process requires several days. On the other 
hand the Woburn Bordeaux having no excess 
of lime is acted upon by the carbon dioxid 
at once and soluble copper is available in a 
short time. 

The increased vigor of plants, particularly 
potatoes, which is noticed when they have 
been sprayd with Bordeaux mixture, is due, 
to the best of our knowledge, to the preven- 
tion of minor insect ravages rather than a 
stimulating action of the very dilute copper 
solution on the chlorophyl. It has been 
shown by Pickering that potato leaves im- 
merst in dilute copper sulfate solution give 
off iron and take on copper and from this it 
was argued that the dilute copper solution 
might have an accelerating effect upon the 
chlorophyl action. Recent work has shown, 
however, that the simpler explanation of in- 



Bordeaux Mixture 75 

sect and disease prevention is the more 
plausible explanation of the apparent stimu- 
lation. Iron is a constituent of chlorophyl. 
The rate at which Bordeaux mixture settles 
is an important matter. Each of the com- 
pounds I to V has a different density, is more 
or less voluminous and settles at a different 
rate from the others. Pickering states that 
the volums occupied by the precipitates after 
standing 15 minutes vary regularly and may 
be represented, approximately, by these num- 
bers, 8(1), 17(11), 86(111), 98(IV), 20(interpo- 
lated) (V). This means that (IV), ordinary 
Bordeaux, is the most voluminous and stays 
in suspension best. Butler* shows that the 
order of mixing and the concentration of solu- 
tions at the time of mixing have a bearing 
on length of time the precipitate stays 'n sus- 
pension and recommends making a dilute 
copper solution and pouring this into a strong 
milk of lime. The d>ections for this exercise 
allow the student to make the copper and lime 
solutions of equal volum and pour one into 
the other indiscriminately. According to 
Butler the methods followd in this exercise 
take second rank in producing desirable volu- 
minous precipitates. 

* Technical Bulletin, No. 8, New Hampshire Experi- 
ment Station; also Phytopathology, 1914. 



76 Preparation of Substances 

QUESTIONS 

(To be answerd in the notebook.) 

5. What amounts of copper sulfate and lime-water 
did you use in making your Woburn Bordeaux? 

6. How many times as much copper sulfate is used 
for ordinary Bordeaux as for the Woburn mixture? 
How does the ordinary Bordeaux mixture differ in 
composition from Woburn? 

7. Give a definition for a basic salt. 

8. How may one test for copper? 

9. What is meant by the expression 4-4-50? 

10. The symbol for the compound (I) CuS04-3CuO 
may be written 4CuO-S03. Rewrite (H), (III) and 
(IV) in a similar manner. Underscore the least basic 
of these compounds. Double underscore the basic 
part of this compound. 

11. What is the use of Bordeaux mixture? How 
does it act? 

12. Figure the amount of calcium sulfate produced 
when the Bordeaux is made using the ratio, IOCUSO4: 
8CaS04, in the equation given in the notes. At a 
volum of 800 cc. what is the maximum amount that 
could dissolv? How much would be left undissolvd? 
Is the undissolvd portion present in Bordeaux mixture? 

13. How much lime is used in this experiment? 
How much is used in the reaction? How much dis- 
solvs in water? What becomes of the remainder? 

14. What substances are in the solid part of the 
Bordeaux? What substances are in solution? 

15. Did you observ the formation of a thin white 
scum on the surface of the ordinary Bordeaux? Ex- 
plain what it is and how it was formd. Write the 
equation showing its formation. 

16. What substances cause the copper to dissolv 
from the Bordeaux mixture? 



Bordeaux Mixture 77 

17. What is meant by copper in a positiv ion? 
Copper in a negativ ion? 

18. In which ion is the copper in copper sulfate? 
Positiv or negativ? 

19. Why is the hberation of soluble copper salt 
from Bordeaux delayd by the presence of lune? 

20. How strong a solution of copper sulfate is 
necessary to kill fungous spores? To kill plants? 



EMULSIONS 

An emulsion contains two immiscible 
liquids and a third colloidal substance mis- 
cible to a greater or less degree with each of 
the other two substances. 

I. KEROSENE EMULSION 

Procedure. — Weigh 5 grams of ordinary 
yellow soap cut into pieces to aid solution and 
dissolv by the aid of heat in 40 cc. of water in 
beaker. When solution is complete add 80 
cc. of kerosene and stir vigorously, or pour 
from one beaker to another, until the emul- 
sion is complete as evinst by the disap- 
pearance of the oil. This is a stock solution 
wh'ch is diluted with 2-10 parts of water as 
required. 

Notebook. 

1. Dilute some of the emulsion and examin a drop 
under the microscope. What is seen? 

2. What substance mixes, to a shght extent, with 
both the kerosene and the water? 

3. Would the decomposition of this substance 
destroy the emulsion? Verify by experiment and tell 
how it was done. 

4. How long, upon standing, before kerosene sepa- 
rates? 

78 



Emulsions 79 

H; MISCIBLE OILS 

There are preparations on the market 
which contain various oils with the emulsify- 
ing agent already added. These are ready 
to use after the addition of water. 

Procedure. — Making sure that all the 
apparatus used is clean, get 10 cc. of a 
miscible oil and dilute it with 12 volums of 
water. If free oil appears on the surface 
after standing a minute clean the appai'atus 
once more and repeat the experiment. 

NOTES 

Kerosene emulsion is an old remedy for in- 
sects that do not chew and consequently can- 
not be poisond. Such sucking insects have 
to be attackt thru their breathing apparatus. 
The aphis is an examp'e. Kerosene alone will 
burn f oUage badly. The emulsion allows the 
use of so little kerosene that no harm is done 
the foliage, there still being sufficient to de- 
stroy the insect. In pract se the happy 
medium is sometimes hard to reach. Kero- 
sene emulsion is practically replaced by solu- 
tions of nicotine sulfate which are obtaind 
from refuse tobacco. 

The miscible oils are a standard remedy for 
scale insects and are appUed in the winter or 
spring before the buds start. It is more 



80 Preparation of Substances 

effective than the lime-sulfur as it creeps 
under the bark reaching all places. One 
thoro application of these oils will eliminate 
scale from an orchard. 

When the miscible oil is not properly 
made by the manufacturer in the first place 
or when the apparatus used in dilution is not 
clean some free oil may separate upon stand- 
ing. If much of any oil appears the material 
is worthless for spraying as the free oil kills 
the twigs and small lims by penetrating the 
bark. 

In the miscible oils the oil and the third 
substance, a colloid in concentrated form, 
have been put together and it only remains 
to add water to make the emulsion. Their 
condition is comparable to eg-yolk which 
consists of 30 per cent fat diffused thru col- 
loidal protein. 

Some idea of emulsions may be gaind from 
the following remarks. 

It is possible to diffuse droplets of kerosene 
thru water by violent agitation. Such sys- 
tems are not stable as the droplets of kerosene 
soon coalesce and separate. This is said to 
be due to the great surface tension which is 
a name for the tendency of small drops to get 
together and get the most mass under the 
least surface. Soap solution — a colloid — 
has a much less surface tension than kero- 



Emulsions 81 

sene and droplets of kerosene mixt with soap 
solution will exist separately for a long time. 
There is a second reason why the kerosene 
will stay emulsified. The droplet is mixt 
with the soap colloid. The concentration of 
the colloid is much greater on the surface 
of the drop than elsewhere. Now when the 
droplet of kerosene and soap has reacht an 
equilibrium, that is, the concentration of the 
soap solution, inside, on the surface, and out- 
side the droplets have come into adjustment, 
a coalition of two droplets of kerosene would 
cause a readjustment of the concentration 
of the solution on the surface which would 
require energy. Consequently the droplet 
once in equilibrium tends to be stable. 



QUESTIONS 
(To be answerd in the notebook.) 

5. What three substances are necessary in an 
emulsion? 

6. Name a colloidal substance. 

7. What is the use of miscible oils? 

8. Which has the greater surface tension soap 
solution or water? 

9. Define the term surface tension. 

10. Where about a droplet of liquid does a colloid, 
when present, tend to concentrate? 



